Celebration time for Victoria Azarenka of Belarus, who opens her WTA Championships by rallying to a 6-7 (11-13), 7-6 (7-2), 6-4 victory against Angelique Kerber of Germany. Matthew Stockman, Getty Images

Serena Williams of the USA shows some emotion during her 6-4, 6-1 victory Tuesday against Angelique Kerber of Germany in her opening match at the WTA Championships in Istanbul. Julian Finney, Getty Images